Digestive system

The human body is a highly complex chemical composition. Most elements of our planet is contained in it. They are members of various chemical compounds from which built cells and tissues. People receive them with food. Water, some minerals and oxygen we perceive as inorganic compounds. All other chemicals the body derives only from organic compounds produced in the bodies of plants and animals. In other words, people (and animals) could not exist at all, if it were not for plants and animals, which only and can be powered.
With nutrition in an organism introduced such a complex matter as proteins, fats and carbohydrates. We know a great many different types of these compounds. This is because each type of organism is composed of proteins, fats and carbohydrates, peculiar only to him. Therefore, it is clear that these substances cannot be assimilated by the organism in the form in which they are contained in food. So they can be perceived, they need to be split, i.e., figuratively speaking, disassemble into simpler components. This is the main role of the digestive system. Part of large and complex molecules, formed as a result of digestion, then go into the blood, which delivers them to the body's cells, where they are built new molecules of proteins, fats and carbohydrates, which is peculiar to human organism. Imagine what a difficult transformation must endure dietary organic matter that they turned into proteins, fats and carbohydrates in the human body. If we tried to reproduce by means of modern chemistry is only the first stage of this process, i.e. that occurs in the digestive system, this would create a large complex of laboratories equipped with sophisticated equipment. "Laboratory" living nature always is many times more economical any modern laboratory. In the conditions of the body the whole complex process of food processing is performed in a short time on a relatively small during the alimentary canal.

Schematically the digestive system can be represented in the form of a tube, which runs throughout the body from the head to the lower end (Fig. 6). This tube can be compared with the pipeline. As you move the content on the "pipeline" of the digestive tract in its various areas consistently performed certain operations of processing of nutrients and the transition of the final products of digestion in the blood.
Tube digestive channel on most of their length is of a General plan of the building! it consists of three layers - outside it forms a sheath of connective tissue, then a layer of smooth muscle, finally, the internal layer is represented by the so-called mucosa. The outer layer separates the digestive tube from the surrounding organs; due to reductions second - muscle layer is promoting its content; the third layer (mucosa) contains cancer, juices which play a vital role in digestion.
On the mucous membrane is necessary to say a few more. Anyone seen mucous language of the inner surface of the lips or cheeks, so its appearance is easy to imagine. This thin soft shell, always having in a healthy person, the color pink and wet surface. It is very rich in blood vessels, from their content in the blood depends on the color of the mucous membrane. In addition, there are a lot glands. One of them is transparent colorless viscous fluid mucus, which moisturizes the surface, helping to slide the contents of the alimentary canal is the so - called mucous glands. Other secrete digestive juices, it is the digestive gland. In addition, in the mucous lot of clusters special protective - lymphoid tissue that forms lymphatic nodules; using them is the struggle with harmful microbes that can get into the body with food and air. It also has a lot of nerve endings, providing its sensitivity. The mucous membrane is lined with epithelial tissue, for in normal conditions it is in contact with the external environment - air, water and food. Through gentle surface of the mucous membrane and tiny blood vessels (called capillaries) penetrate (absorbed), water and dissolved substances. This is the General plan of structure of the digestive tube.
Above we have said that the digestion occurs gradually move it through the GI tract, so every part of him, as it is specialized in the execution of specific phases of the process. In this regard, in the presence of the General plan of the structure of certain parts of the digestive tract has its own individual features and present a number of consecutive hollow organs. So, the initial division of the digestive tract presents oral cavity. It is followed by the throat, then the esophagus, stomach and small intestine *, followed by the colon (see Fig. 6).

* Starting small intestine, following the stomach, called the duodenum.